四川盆地(di)聚居著四川省(sheng)和重慶市大部分人(ren)口、居民主(zhu)要為漢族巴(ba)蜀民系。是中(zhong)國(guo)和世界上人(ren)口最多的區域之一。
中(zhong)國(guo)(guo)著名(ming)紅(hong)層盆(pen)地,中(zhong)國(guo)(guo)各大盆(pen)地中(zhong)形態最典型、緯度最南、海(hai)拔最低的盆(pen)地。位于長江上(shang)游地區,海(hai)拔500米左右,長江把它和東海(hai)一脈(mo)相(xiang)連,它是中(zhong)國(guo)(guo)最大的外流盆(pen)地。
四(si)川(chuan)(chuan)盆(pen)(pen)地(di)(di)的(de)(de)面(mian)積(ji)約(yue)26萬(wan)余(yu)平方(fang)(fang)(fang)千(qian)米(mi)(面(mian)積(ji)是(shi)(shi)居第五第六位的(de)(de)兩湖盆(pen)(pen)地(di)(di)和(he)(he)銀額(e)盆(pen)(pen)地(di)(di)的(de)(de)兩倍),占四(si)川(chuan)(chuan)省面(mian)積(ji)的(de)(de)46%。四(si)川(chuan)(chuan)盆(pen)(pen)地(di)(di)西(xi)(xi)依(yi)青藏高原(yuan)和(he)(he)橫斷山(shan)(shan)(shan)脈,北(bei)(bei)(bei)近秦(qin)巴山(shan)(shan)(shan)脈,與(yu)漢中盆(pen)(pen)地(di)(di)相(xiang)望,東(dong)(dong)接湘鄂西(xi)(xi)山(shan)(shan)(shan)地(di)(di),南(nan)連(lian)云(yun)貴高原(yuan),盆(pen)(pen)地(di)(di)北(bei)(bei)(bei)緣(yuan)(yuan)米(mi)倉山(shan)(shan)(shan),南(nan)緣(yuan)(yuan)大婁山(shan)(shan)(shan),東(dong)(dong)緣(yuan)(yuan)巫山(shan)(shan)(shan),西(xi)(xi)緣(yuan)(yuan)邛(qiong)崍山(shan)(shan)(shan),西(xi)(xi)北(bei)(bei)(bei)邊(bian)(bian)緣(yuan)(yuan)龍(long)門(men)(men)山(shan)(shan)(shan),東(dong)(dong)北(bei)(bei)(bei)邊(bian)(bian)緣(yuan)(yuan)大巴山(shan)(shan)(shan),西(xi)(xi)南(nan)邊(bian)(bian)緣(yuan)(yuan)大涼山(shan)(shan)(shan),東(dong)(dong)南(nan)邊(bian)(bian)緣(yuan)(yuan)相(xiang)望于武陵山(shan)(shan)(shan)。這里的(de)(de)巖(yan)石,主要由紫(zi)紅色(se)砂巖(yan)和(he)(he)頁(ye)巖(yan)組成。這兩種巖(yan)石極易風化發育成紫(zi)色(se)土(tu)。紫(zi)色(se)土(tu)含有豐(feng)富的(de)(de)鈣、磷、鉀等營養元素,是(shi)(shi)南(nan)方(fang)(fang)(fang)最肥沃(wo)的(de)(de)自(zi)然土(tu)壤(rang)。四(si)川(chuan)(chuan)盆(pen)(pen)地(di)(di)是(shi)(shi)全國紫(zi)色(se)土(tu)分(fen)布最集中的(de)(de)地(di)(di)方(fang)(fang)(fang),向(xiang)有“紫(zi)色(se)盆(pen)(pen)地(di)(di)”的(de)(de)美稱。四(si)川(chuan)(chuan)盆(pen)(pen)地(di)(di)底部(bu)面(mian)積(ji)約(yue)16萬(wan)多平方(fang)(fang)(fang)千(qian)米(mi),按其地(di)(di)理差異(yi),自(zi)西(xi)(xi)向(xiang)東(dong)(dong)又可分(fen)為成都平原(yuan)、川(chuan)(chuan)中丘陵和(he)(he)川(chuan)(chuan)東(dong)(dong)平行(xing)嶺谷三部(bu)分(fen)。成都平原(yuan)西(xi)(xi)方(fang)(fang)(fang)是(shi)(shi)龍(long)門(men)(men)山(shan)(shan)(shan)脈,東(dong)(dong)方(fang)(fang)(fang)是(shi)(shi)龍(long)泉山(shan)(shan)(shan)脈。
四川盆(pen)地可(ke)明顯分為邊緣山(shan)地和(he)盆(pen)地底部兩大部分,其面積分別約為10萬(wan)多和(he)16多萬(wan)平(ping)方(fang)公里。邊緣山(shan)地多中山(shan)和(he)低山(shan)。
景觀各要素過渡(du)性明顯,如動植(zhi)物(wu)組成(cheng)上(shang)(shang)分(fen)別滲透了華中(zhong)區(qu)、西南區(qu)、青藏高原區(qu)和華北(bei)區(qu)的成(cheng)分(fen)。邊(bian)緣(yuan)(yuan)山地(di)區(qu)從下而上(shang)(shang)一般具有2~5個垂直(zhi)自然分(fen)帶。邊(bian)緣(yuan)(yuan)山地(di)是四(si)川多(duo)種經(jing)濟林木和用材林基地(di)。農業上(shang)(shang)水(shui)土流失較(jiao)為(wei)嚴重。盆地(di)底部多(duo)丘陵、低山和平(ping)原。地(di)表(biao)組成(cheng)物(wu)質新而單一,多(duo)砂泥巖與第四(si)紀沉積(ji)物(wu)。氣候上(shang)(shang)屬中(zhong)亞熱帶,熱量(liang)(liang)遠比邊(bian)緣(yuan)(yuan)山地(di)為(wei)高,但降水(shui)量(liang)(liang)不及邊(bian)緣(yuan)(yuan)山地(di)。植(zhi)被為(wei)人工的次生林木所代替,覆被率低,耕(geng)地(di)連片,夏伏旱和洪澇是這一地(di)區(qu)最(zui)大災害。
盆地(di)(di)內部地(di)(di)形地(di)(di)貌(mao)顯示出明顯的(de)三(san)分特點,即盆西(xi)平原地(di)(di)貌(mao)、盆中丘陵地(di)(di)貌(mao)和(he)盆東山地(di)(di)地(di)(di)貌(mao),三(san)者(zhe)以龍泉山和(he)華鎣(ying)山為界(jie)。
四川盆地(di)(di)(di)(di)其輪廓(kuo)形(xing)態總體近(jin)(jin)似長方形(xing),形(xing)似信封(feng)狀,右傾斜置(zhi)在亞(ya)洲大(da)陸,因此被地(di)(di)(di)(di)理學(xue)者稱之(zhi)為信封(feng)盆地(di)(di)(di)(di)。信封(feng)盆地(di)(di)(di)(di)東部頂點云(yun)陽(靠(kao)近(jin)(jin)萬(wan)州(zhou)),南(nan)部頂點敘永(靠(kao)近(jin)(jin)遵(zun)義),西(xi)部頂點雅安,北(bei)部頂點廣元。信封(feng)盆地(di)(di)(di)(di)幾何中心(xin)(xin)城市(shi)遂(sui)寧(幾何中心(xin)(xin)點大(da)致在蓬(peng)溪南(nan)部地(di)(di)(di)(di)區(qu)),中北(bei)部(內頂角)中心(xin)(xin)城市(shi)南(nan)充,中南(nan)部內頂角安岳。
四川盆地西部(bu)的(de)(de)成(cheng)都和東南部(bu)的(de)(de)重(zhong)慶皆為國家中心城市(shi)。
四(si)川盆(pen)地由盆(pen)周山地和盆(pen)地底部構成(cheng)。
盆周東部(bu)(bu)為長江(jiang)三峽,南部(bu)(bu)為云貴高原,西部(bu)(bu)為青藏高原,北部(bu)(bu)為大巴山。
盆地底部主要分(fen)為川(chuan)東(dong)平(ping)行(xing)嶺(ling)谷、川(chuan)中(zhong)丘(qiu)陵和(he)川(chuan)西成都(dou)平(ping)原(yuan)三部分(fen)。龍泉(quan)山(shan)(shan)是成都(dou)平(ping)原(yuan)和(he)川(chuan)中(zhong)丘(qiu)陵的界(jie)山(shan)(shan),華(hua)鎣山(shan)(shan)是川(chuan)中(zhong)丘(qiu)陵和(he)川(chuan)東(dong)平(ping)行(xing)嶺(ling)谷的界(jie)山(shan)(shan)。
(1)在龍泉山和龍門(men)山、邛(qiong)崍山之間的(de)盆西(xi)平(ping)原(yuan),系斷(duan)裂下陷由(you)岷江(jiang)水系的(de)河(he)流沖積(ji)而(er)成(cheng),面積(ji)約8000平(ping)方千米(mi)(mi),為我國西(xi)南(nan)(nan)最大的(de)平(ping)原(yuan),因成(cheng)都位于(yu)平(ping)原(yuan)之中, 故稱成(cheng)都平(ping)原(yuan)。成(cheng)都平(ping)原(yuan)海拔460米(mi)(mi)~750米(mi)(mi),地勢由(you)西(xi)北向東南(nan)(nan)傾斜,地表(biao)平(ping)坦,相對高(gao)差一般(ban)不(bu)超(chao)過30米(mi)(mi)~50米(mi)(mi),它由(you)岷江(jiang)、沱江(jiang)、涪(fu)江(jiang)、青(qing)衣江(jiang)等八條河(he)流沖積(ji)聯(lian)綴(zhui)而(er)成(cheng),土壤肥沃,河(he)渠(qu)稠密,有著名的(de)都江(jiang)堰自(zi)流灌溉,自(zi)古以來素有“天(tian)府”之稱。
(2)在龍泉(quan)山(shan)(shan)和(he)華鎣山(shan)(shan)之(zhi)間的(de)盆中丘(qiu)陵(ling),地(di)勢(shi)低(di)矮,海拔大(da)多在300米(mi)~500米(mi)之(zhi)間,相對高(gao)差50米(mi)~150米(mi),地(di)勢(shi)由北向南傾斜,巖層近于水(shui)平,在流水(shui)的(de)長(chang)期(qi)侵蝕切割作(zuo)(zuo)用下,形成臺階(jie)狀(zhuang)的(de)方(fang)山(shan)(shan)丘(qiu)陵(ling),南部多淺(qian)丘(qiu),北部多深丘(qiu)。丘(qiu)陵(ling)地(di)表軟硬相間的(de)紫紅色砂、頁巖極易風化為紫色土,富含磷鉀,自然(ran)肥(fei)力較高(gao),宜種性廣,是四川全(quan)省(sheng)糧食、經濟作(zuo)(zuo)物主產區。
(3)華(hua)鎣(ying)山(shan)(shan)以(yi)東(dong)為(wei)(wei)盆東(dong)平(ping)行嶺(ling)谷(gu)區,由多條近東(dong)北西南走向(xiang)的(de)條狀背斜山(shan)(shan)地(di)與(yu)向(xiang)斜寬(kuan)谷(gu)組成,山(shan)(shan)地(di)陡而(er)窄(zhai),高700米(mi)(mi)(mi)-1000米(mi)(mi)(mi),其中,華(hua)鎣(ying)山(shan)(shan)高1705米(mi)(mi)(mi),為(wei)(wei)盆地(di)底部最高峰。山(shan)(shan)地(di)頂部的(de)石灰巖被雨水溶蝕(shi)后(hou),常成凹槽,故山(shan)(shan)地(di)大多具有“一(yi)(yi)山(shan)(shan)二嶺(ling)一(yi)(yi)槽”或(huo)“一(yi)(yi)山(shan)(shan)三嶺(ling)二槽”的(de)特色。山(shan)(shan)嶺(ling)間的(de)谷(gu)地(di)寬(kuan)而(er)緩,海拔300米(mi)(mi)(mi)~500米(mi)(mi)(mi),其間丘陵、平(ping)壩交錯分布,是(shi)平(ping)行嶺(ling)谷(gu)區工農業生產主要地(di)區。
四川盆地邊(bian)緣山地區屬強烈上升的褶皺(zhou)帶。
地貌顯著特征是,海拔較高(gao),過渡性(xing)明顯,均(jun)為一(yi)(yi)系列中山(shan)(shan)和低山(shan)(shan)所(suo)圍繞。盆地北緣米(mi)(mi)(mi)倉山(shan)(shan)、大(da)巴(ba)山(shan)(shan)近(jin)東西走向(xiang),是秦(qin)巴(ba)山(shan)(shan)地南(nan)翼部分,海拔一(yi)(yi)般在1500米(mi)(mi)(mi)~2200米(mi)(mi)(mi)之間,山(shan)(shan)勢(shi)雄偉,山(shan)(shan)坡陡峭,溝谷深切,相對高(gao)差可達500米(mi)(mi)(mi)~1000米(mi)(mi)(mi);南(nan)緣大(da)婁山(shan)(shan)屬氣勢(shi)磅礴的云貴高(gao)原(yuan)之一(yi)(yi)部分;西緣有龍門山(shan)(shan)、邛崍山(shan)(shan)、峨眉山(shan)(shan),山(shan)(shan)脊(ji)海拔都在1500米(mi)(mi)(mi)至~3000米(mi)(mi)(mi)以(yi)上(shang),相對高(gao)差可達1000米(mi)(mi)(mi),屬中國(guo)地勢(shi)第一(yi)(yi)級階梯。峨眉山(shan)(shan)頂峰高(gao)3099米(mi)(mi)(mi),與附近(jin)的平原(yuan)相對高(gao)差達2660米(mi)(mi)(mi),山(shan)(shan)勢(shi)巍峨秀麗,為中國(guo)四(si)大(da)佛教名山(shan)(shan)之一(yi)(yi)。
四周為海拔2000~3000米(mi)的山(shan)脈和高原(yuan)所環繞(rao),北面是大巴山(shan)、米(mi)倉山(shan)、龍門山(shan),西(xi)面是青藏高原(yuan)邊緣的邛崍山(shan)、大涼山(shan),南面是大婁山(shan),東(dong)面是巫(wu)山(shan)。
無論從(cong)構造還(huan)是(shi)人(ren)地(di)貌上(shang)看(kan),四(si)川盆(pen)(pen)(pen)(pen)(pen)地(di)都是(shi)一(yi)個(ge)典型(xing)的(de)(de)(de)(de)盆(pen)(pen)(pen)(pen)(pen)地(di)。它從(cong)震旦紀以來就是(shi)地(di)殼比(bi)較穩定的(de)(de)(de)(de)大型(xing)拗陷(xian)區(qu)。晚三(san)迭紀的(de)(de)(de)(de)印支運動(dong)中(zhong)(zhong)成為一(yi)個(ge)內(nei)(nei)陸(lu)湖盆(pen)(pen)(pen)(pen)(pen),但范圍要比(bi)今日的(de)(de)(de)(de)四(si)川大得多,中(zhong)(zhong)生(sheng)代(dai)堆積了厚達(da)3000~4000米的(de)(de)(de)(de)紫紅色的(de)(de)(de)(de)砂巖(yan)和頁巖(yan),因此人(ren)們又(you)稱它為“紅色盆(pen)(pen)(pen)(pen)(pen)地(di)”或“紫色盆(pen)(pen)(pen)(pen)(pen)地(di)”。中(zhong)(zhong)生(sheng)代(dai)末(mo)期的(de)(de)(de)(de)四(si)川運動(dong)使盆(pen)(pen)(pen)(pen)(pen)地(di)周(zhou)(zhou)圍褶皺成山(shan)(shan),中(zhong)(zhong)間(jian)相對下陷(xian),輪(lun)廓(kuo)基本形(xing)(xing)成,盆(pen)(pen)(pen)(pen)(pen)地(di)內(nei)(nei)部(bu)地(di)層也發生(sheng)大規模的(de)(de)(de)(de)變(bian)形(xing)(xing)。東(dong)部(bu)出現一(yi)組北東(dong)向的(de)(de)(de)(de)褶皺,稱盆(pen)(pen)(pen)(pen)(pen)東(dong)褶皺帶(dai);中(zhong)(zhong)部(bu)形(xing)(xing)成穹窿(long)構造,稱盆(pen)(pen)(pen)(pen)(pen)中(zhong)(zhong)穹窿(long)帶(dai);西部(bu)表(biao)現成為盆(pen)(pen)(pen)(pen)(pen)地(di)沉陷(xian)帶(dai),為今天盆(pen)(pen)(pen)(pen)(pen)地(di)的(de)(de)(de)(de)三(san)個(ge)地(di)貌區(qu)奠(dian)定了基礎。新生(sheng)代(dai)的(de)(de)(de)(de)喜馬(ma)拉雅(ya)運動(dong)使周(zhou)(zhou)圍山(shan)(shan)地(di)再次(ci)(ci)上(shang)升,盆(pen)(pen)(pen)(pen)(pen)地(di)再次(ci)(ci)相對下陷(xian), 成都一(yi)帶(dai)下陷(xian)更深。同時,長(chang)江(jiang)切穿巫山(shan)(shan),滾滾東(dong)流(liu),完成了統(tong)一(yi)的(de)(de)(de)(de)長(chang)江(jiang)水系,使內(nei)(nei)流(liu)盆(pen)(pen)(pen)(pen)(pen)地(di)轉(zhuan)變(bian)為外(wai)流(liu)盆(pen)(pen)(pen)(pen)(pen)地(di)。四(si)川盆(pen)(pen)(pen)(pen)(pen)地(di)可(ke)明顯分為邊緣山(shan)(shan)地(di)和盆(pen)(pen)(pen)(pen)(pen)地(di)底部(bu)兩(liang)大部(bu)分,其面積分別約為10萬多和16萬多平(ping)方千米。 四(si)川盆(pen)(pen)(pen)(pen)(pen)地(di)是(shi)我國最大的(de)(de)(de)(de)外(wai)流(liu)盆(pen)(pen)(pen)(pen)(pen)地(di),面積26萬多平(ping)方千米。四(si)川盆(pen)(pen)(pen)(pen)(pen)地(di)內(nei)(nei)部(bu)丘陵(ling)、平(ping)原交錯(cuo),地(di)勢北高(gao)南低(di)。由于地(di)表(biao)形(xing)(xing)態的(de)(de)(de)(de)不(bu)同,以華鎣山(shan)(shan)、龍泉山(shan)(shan)為界。
盆底(di)可分為(wei)三部分:
①華鎣山以東為(wei)大(da)致(zhi)平行(xing)的(de)川(chuan)東嶺谷,由東北(bei)—西南走向(xiang)的(de)許(xu)多(duo)條狀山體組成,海拔一般在700~800米(mi),谷地中(zhong)多(duo)低丘與平壩(ba),海拔200~500米(mi),是川(chuan)東農業和人口集中(zhong)的(de)地方。
②華鎣(ying)山(shan)(shan)和龍泉(quan)山(shan)(shan)之(zhi)間為方(fang)山(shan)(shan)丘陵(ling),即川中丘陵(ling)。區內(nei)由于紫紅(hong)色砂(sha)頁巖傾角(jiao)平緩,受切(qie)割后形成(cheng)大片方(fang)山(shan)(shan)式丘陵(ling)。海拔350~450米(mi),相(xiang)對高度幾十米(mi)。當地勞動(dong)人民利用方(fang)山(shan)(shan)山(shan)(shan)丘土層(ceng)深厚(hou)的特點(dian),把(ba)梯田(tian)一直修到山(shan)(shan)頂。
③龍(long)泉山(shan)以西(xi)(xi)為(wei)(wei)平原(yuan)。稱為(wei)(wei)川西(xi)(xi)平原(yuan)或成都平原(yuan),面積6000多平方千米,是四川盆地最大的平原(yuan),也是西(xi)(xi)南地區最大的平原(yuan),海拔約600米。
四(si)(si)川(chuan)(chuan)盆(pen)(pen)(pen)(pen)地(di)(di)屬揚子準(zhun)地(di)(di)臺四(si)(si)川(chuan)(chuan)臺坳。古生(sheng)代時相對隆起(qi),缺乏泥(ni)盆(pen)(pen)(pen)(pen)系(xi)和(he)石(shi)(shi)炭系(xi)。印支運動(dong)轉(zhuan)換為(wei)(wei)(wei)大(da)型拗陷,晚燕山(shan)運動(dong),特(te)別是(shi)喜馬(ma)拉雅運動(dong)后(hou)發(fa)(fa)生(sheng)褶皺隆起(qi)。盆(pen)(pen)(pen)(pen)地(di)(di)的(de)(de)(de)格局(ju)主要(yao)受(shou)北東—南(nan)(nan)西向(xiang)及(ji)北西向(xiang)兩(liang)(liang)條構(gou)造線控制,構(gou)成(cheng)了典(dian)型的(de)(de)(de)菱(ling)形盆(pen)(pen)(pen)(pen)地(di)(di),四(si)(si)川(chuan)(chuan)廣元、四(si)(si)川(chuan)(chuan)雅安、四(si)(si)川(chuan)(chuan)敘永為(wei)(wei)(wei)菱(ling)形的(de)(de)(de)四(si)(si)頂(ding)點,東西兩(liang)(liang)邊(bian)(bian)稍長,為(wei)(wei)(wei)380~430公(gong)里,南(nan)(nan)北兩(liang)(liang)邊(bian)(bian)略短,為(wei)(wei)(wei)310~330公(gong)里。以上(shang)菱(ling)形四(si)(si)頂(ding)點的(de)(de)(de)連(lian)線與(yu)盆(pen)(pen)(pen)(pen)地(di)(di)內650~750米(mi)(mi)(mi)(mi)(mi)的(de)(de)(de)等(deng)(deng)高線大(da)體相當,盆(pen)(pen)(pen)(pen)地(di)(di)底部(bu)與(yu)邊(bian)(bian)緣(yuan)(yuan)山(shan)地(di)(di)也(ye)以此(ci)為(wei)(wei)(wei)分(fen)界(jie)。四(si)(si)川(chuan)(chuan)盆(pen)(pen)(pen)(pen)地(di)(di)在(zai)距今1.4億年以前,還是(shi)內陸湖盆(pen)(pen)(pen)(pen)。至(zhi)距今6.6千萬年時,盆(pen)(pen)(pen)(pen)地(di)(di)邊(bian)(bian)緣(yuan)(yuan)山(shan)地(di)(di)迅速隆升,長江中(zhong)上(shang)游水(shui)(shui)系(xi)開始溝通。盆(pen)(pen)(pen)(pen)地(di)(di)內湖水(shui)(shui)東瀉奠定(ding)了現今之地(di)(di)貌(mao)形態。盆(pen)(pen)(pen)(pen)地(di)(di)邊(bian)(bian)緣(yuan)(yuan)多低(di)山(shan)和(he)中(zhong)山(shan),山(shan)勢陡峻,發(fa)(fa)源盆(pen)(pen)(pen)(pen)地(di)(di)邊(bian)(bian)緣(yuan)(yuan)山(shan)地(di)(di)的(de)(de)(de)河(he)流(liu)(liu)大(da)多為(wei)(wei)(wei)“V”型谷(gu)(gu),嶺(ling)谷(gu)(gu)高差都逾500~1 000米(mi)(mi)(mi)(mi)(mi), 地(di)(di)表崎(qi)嶇,故歷史上(shang)就有(you)(you)(you)“蜀道難,難于上(shang)青(qing)天(tian)”之說。山(shan)脊海拔大(da)多在(zai)2000~3000米(mi)(mi)(mi)(mi)(mi),西北部(bu)與(yu)西部(bu)可(ke)超(chao)過(guo)3000~4000米(mi)(mi)(mi)(mi)(mi),如龍(long)門山(shan)4984米(mi)(mi)(mi)(mi)(mi),峨(e)眉(mei)山(shan)3099米(mi)(mi)(mi)(mi)(mi),小相嶺(ling)4 791米(mi)(mi)(mi)(mi)(mi)。地(di)(di)表廣泛(fan)出露古生(sheng)代及(ji)其以前的(de)(de)(de)石(shi)(shi)灰巖(yan)(yan),其次為(wei)(wei)(wei)板巖(yan)(yan)、片(pian)巖(yan)(yan)、結(jie)晶灰巖(yan)(yan)、石(shi)(shi)英巖(yan)(yan)、砂泥(ni)巖(yan)(yan)和(he)礫巖(yan)(yan),局(ju)部(bu)有(you)(you)(you)花崗巖(yan)(yan)和(he)玄武巖(yan)(yan)。石(shi)(shi)灰巖(yan)(yan)分(fen)布區(qu)(qu)可(ke)見石(shi)(shi)林、溶洞(dong)(dong)、暗(an)河(he)、槽谷(gu)(gu)等(deng)(deng)喀(ka)斯(si)特(te)地(di)(di)貌(mao),盆(pen)(pen)(pen)(pen)地(di)(di)南(nan)(nan)緣(yuan)(yuan)興(xing)文縣素有(you)(you)(you)“石(shi)(shi)林洞(dong)(dong)鄉(xiang)”之稱(見興(xing)文石(shi)(shi)林)。巫山(shan)十(shi)二(er)峰和(he)金佛山(shan)等(deng)(deng)名山(shan)主要(yao)也(ye)由(you)石(shi)(shi)灰巖(yan)(yan)發(fa)(fa)育而(er)成(cheng)。由(you)石(shi)(shi)灰巖(yan)(yan)、玄武巖(yan)(yan)、花崗巖(yan)(yan)等(deng)(deng)組成(cheng)的(de)(de)(de)峨(e)眉(mei)山(shan)及(ji)由(you)砂泥(ni)巖(yan)(yan)、礫巖(yan)(yan)組成(cheng)的(de)(de)(de)青(qing)城山(shan),素有(you)(you)(you)“峨(e)眉(mei)天(tian)下秀”、“青(qing)城天(tian)下幽”之稱,為(wei)(wei)(wei)中(zhong)國著名游覽勝地(di)(di)。盆(pen)(pen)(pen)(pen)地(di)(di)底部(bu)海拔多數(shu)在(zai)250~700米(mi)(mi)(mi)(mi)(mi),地(di)(di)勢東南(nan)(nan)傾(qing),盆(pen)(pen)(pen)(pen)地(di)(di)內各(ge)河(he)流(liu)(liu)均(jun)由(you)邊(bian)(bian)緣(yuan)(yuan)山(shan)地(di)(di)匯聚盆(pen)(pen)(pen)(pen)地(di)(di)底部(bu)的(de)(de)(de)長江干(gan)流(liu)(liu),形成(cheng)向(xiang)心(xin)狀(zhuang)水(shui)(shui)系(xi)。地(di)(di)表為(wei)(wei)(wei)大(da)面(mian)積的(de)(de)(de)中(zhong)生(sheng)代紫紅(hong)色砂巖(yan)(yan)與(yu)泥(ni)巖(yan)(yan)所覆蓋,故稱為(wei)(wei)(wei)“紅(hong)層(ceng)盆(pen)(pen)(pen)(pen)地(di)(di)”,是(shi)中(zhong)國中(zhong)生(sheng)代陸相紅(hong)層(ceng)分(fen)布最集中(zhong)地(di)(di)區(qu)(qu)。四(si)(si)川(chuan)(chuan)盆(pen)(pen)(pen)(pen)地(di)(di)為(wei)(wei)(wei)丘陵(ling)性盆(pen)(pen)(pen)(pen)地(di)(di),底部(bu)以丘陵(ling)為(wei)(wei)(wei)主,次為(wei)(wei)(wei)低(di)山(shan)和(he)平原。
四川盆地(di)屬揚子(zi)陸(lu)臺(tai)一(yi)(yi)部分,稱為四川陸(lu)臺(tai),屬較(jiao)穩(wen)定的(de)(de)地(di)區(qu),但仍經過兩次(ci)大規(gui)模的(de)(de)海(hai)浸(jin)。第一(yi)(yi)次(ci)從5億多(duo)年前(qian)的(de)(de)寒武(wu)紀開始,延續(xu)(xu)到3.7億多(duo)年的(de)(de)志(zhi)留(liu)紀,不斷下陷(xian)成了海(hai)洋盆地(di),志(zhi)留(liu)紀時發(fa)生(sheng)加里東運動,除了西部的(de)(de)龍門山地(di)槽繼續(xu)(xu)下陷(xian)外,其(qi)余地(di)區(qu)上升為陸(lu)。2.7億年前(qian)的(de)(de)石炭紀末,發(fa)生(sheng)范圍更大的(de)(de)第二次(ci)海(hai)浸(jin),盆地(di)再次(ci)為海(hai)洋占(zhan)據。二疊(die)(die)紀時海(hai)陸(lu)交(jiao)替,形成重(zhong)慶附近的(de)(de)南(nan)酮(tong)、松(song)藻(zao)、天(tian)府等煤礦。二疊(die)(die)紀末,盆地(di)西部巖漿噴出(chu),峨眉山小金(jin)頂及清(qing)音(yin)閣(ge)一(yi)(yi)帶(dai)的(de)(de)玄武(wu)巖就(jiu)在這時生(sheng)成。
距今1.9億(yi)年的三疊紀,“印支運(yun)動”使盆(pen)(pen)地邊緣(yuan)逐(zhu)漸(jian)隆起成(cheng)山(shan),被(bei)海水(shui)(shui)淹沒的地區逐(zhu)漸(jian)上升(sheng)成(cheng)陸(lu),由海盆(pen)(pen)轉為(wei)湖(hu)盆(pen)(pen)。當(dang)時湖(hu)水(shui)(shui)幾乎占據現今四川(chuan)盆(pen)(pen)地的全境,稱(cheng)為(wei)“蜀湖(hu)”,從此(ci)結(jie)束了海浸的歷史。在(zai)中生(sheng)代漫(man)長的1億(yi)多年里,盆(pen)(pen)地氣候(hou)溫(wen)暖濕潤(run),到(dao)處生(sheng)長蕨類、蘇鐵和裸子植(zhi)物(wu),是(shi)又一個成(cheng)煤期,永(yong)榮煤礦即在(zai)三疊紀和侏羅(luo)紀時形(xing)成(cheng)。東起長壽、墊江,西到(dao)江油、邛崍(lai),北抵大巴山(shan)麓,南(nan)到(dao)貴州(zhou)赤(chi)水(shui)(shui),還是(shi)天然氣富集區。這一時期爬行動物(wu)恐(kong)龍(long)(long)稱(cheng)霸一時。1957年在(zai)合州(zhou)發現的“合州(zhou)馬門溪龍(long)(long)”身長22米(mi),高3.5米(mi),是(shi)中國(guo)亞洲最(zui)大和最(zui)完整的恐(kong)龍(long)(long)化石(shi)。
7000萬年(nian)前的(de)(de)(de)(de)白堊(e)紀(ji)末期,發(fa)(fa)(fa)生又(you)一次強烈(lie)的(de)(de)(de)(de)地(di)(di)(di)(di)殼(ke)運(yun)動(dong)(dong)“燕山(shan)(shan)(shan)(shan)運(yun)動(dong)(dong)”。盆(pen)(pen)地(di)(di)(di)(di)四(si)周山(shan)(shan)(shan)(shan)地(di)(di)(di)(di)繼續隆起,同(tong)時(shi)產(chan)生不少大(da)(da)(da)斷(duan)層(ceng)(ceng),如西(xi)部(bu)(bu)的(de)(de)(de)(de)龍門(men)山(shan)(shan)(shan)(shan)大(da)(da)(da)斷(duan)層(ceng)(ceng)和(he)東部(bu)(bu)的(de)(de)(de)(de)華(hua)瑩山(shan)(shan)(shan)(shan)大(da)(da)(da)斷(duan)層(ceng)(ceng),把盆(pen)(pen)地(di)(di)(di)(di)分為(wei)三部(bu)(bu)分。蜀(shu)湖(hu)縮(suo)小(xiao)(xiao)為(wei)僅有2萬平方公里的(de)(de)(de)(de)蜀(shu)湖(hu)。封閉(bi)的(de)(de)(de)(de)盆(pen)(pen)地(di)(di)(di)(di)地(di)(di)(di)(di)形(xing)及(ji)急(ji)劇(ju)縮(suo)小(xiao)(xiao)的(de)(de)(de)(de)水面,使(shi)氣候逐漸變(bian)得干熱,沉(chen)(chen)積(ji)物(wu)(wu)由(you)(you)海相、海陸(lu)交替相變(bian)為(wei)陸(lu)相,大(da)(da)(da)量風化、侵(qin)蝕、剝(bo)蝕的(de)(de)(de)(de)物(wu)(wu)質(zhi)在(zai)盆(pen)(pen)地(di)(di)(di)(di)堆(dui)(dui)積(ji)了(le)數(shu)千米厚,形(xing)成紅色和(he)紫紅色的(de)(de)(de)(de)砂(sha)、泥、頁巖。裸子(zi)植物(wu)(wu)不斷(duan)衰(shuai)退(tui),恐龍滅絕了(le)。內(nei)陸(lu)湖(hu)泊在(zai)干燥條件(jian)下,經(jing)強烈(lie)蒸(zheng)發(fa)(fa)(fa),濃度(du)增大(da)(da)(da),鹽(yan)分不斷(duan)積(ji)累,形(xing)成鹽(yan)湖(hu),后來泥沙掩埋而保存于地(di)(di)(di)(di)層(ceng)(ceng)之(zhi)(zhi)中,經(jing)過(guo)漫長的(de)(de)(de)(de)地(di)(di)(di)(di)質(zhi)作用形(xing)成巖層(ceng)(ceng),自(zi)貢(gong)一帶(dai)是(shi)著名的(de)(de)(de)(de)井鹽(yan)產(chan)地(di)(di)(di)(di)。 2000多萬年(nian)前的(de)(de)(de)(de)新(xin)第(di)三紀(ji),受喜馬(ma)拉(la)雅造山(shan)(shan)(shan)(shan)運(yun)動(dong)(dong)的(de)(de)(de)(de)影響。距今二、三百萬年(nian)的(de)(de)(de)(de)第(di)四(si)紀(ji),地(di)(di)(di)(di)殼(ke)再次發(fa)(fa)(fa)生構造運(yun)動(dong)(dong)。從(cong)而,四(si)川(chuan)盆(pen)(pen)地(di)(di)(di)(di)由(you)(you)內(nei)流(liu)盆(pen)(pen)地(di)(di)(di)(di)變(bian)為(wei)外流(liu)陸(lu)盆(pen)(pen),由(you)(you)封閉(bi)的(de)(de)(de)(de)內(nei)流(liu)區(qu)(qu)變(bian)為(wei)外流(liu)區(qu)(qu),由(you)(you)以堆(dui)(dui)積(ji)為(wei)主變(bian)為(wei)侵(qin)蝕為(wei)主,經(jing)歷了(le)海盆(pen)(pen)——湖(hu)盆(pen)(pen)——陸(lu)盆(pen)(pen)的(de)(de)(de)(de)滄桑(sang)之(zhi)(zhi)變(bian)。 第(di)四(si)紀(ji)是(shi)冰(bing)川(chuan)廣布的(de)(de)(de)(de)時(shi)代,盆(pen)(pen)地(di)(di)(di)(di)西(xi)北山(shan)(shan)(shan)(shan)地(di)(di)(di)(di)發(fa)(fa)(fa)育大(da)(da)(da)量冰(bing)川(chuan)。冰(bing)川(chuan)消(xiao)融后,大(da)(da)(da)量沉(chen)(chen)積(ji)物(wu)(wu)由(you)(you)岷江、沱江等攜帶(dai),堆(dui)(dui)積(ji)在(zai)西(xi)部(bu)(bu)的(de)(de)(de)(de)凹陷區(qu)(qu),即以前的(de)(de)(de)(de)蜀(shu)湖(hu)之(zhi)(zhi)中,最(zui)終形(xing)成了(le)成都平原(yuan)。 四(si)川(chuan)盆(pen)(pen)地(di)(di)(di)(di)地(di)(di)(di)(di)貌豐富,平原(yuan)7%,丘(qiu)陵52%,低山(shan)(shan)(shan)(shan)41%。
四(si)川(chuan)盆(pen)地中植(zhi)物近萬種(zhong),古老(lao)而特(te)有(you)種(zhong)之多為中國其(qi)他地區所不及。在盆(pen)地邊緣山(shan)地及盆(pen)東平行嶺(ling)谷尚可(ke)見(jian)水(shui)杉(shan)(shan)、銀杉(shan)(shan)、鵝掌楸、檫木(mu)(mu)、三尖杉(shan)(shan)、珙桐、水(shui)青(qing)樹(shu)、連香樹(shu)、領春木(mu)(mu)、金錢槭、蠟梅、杜仲、紅豆杉(shan)(shan)、鐘萼木(mu)(mu)、福建柏(bo)、穗花(hua)杉(shan)(shan)、崖柏(bo)、木(mu)(mu)瓜紅等(deng)珍(zhen)稀孑遺植(zhi)物與特(te)有(you)種(zhong)。在濕熱河谷可(ke)見(jian)桫(suo)欏、小羽桫(suo)欏、烏毛(mao)蕨、華南(nan)紫(zi)萁、里白等(deng)古熱帶孑遺植(zhi)物。 四(si)川(chuan)盆(pen)地的地帶性植(zhi)被是(shi)(shi)亞熱帶常綠(lv)闊(kuo)葉(xie)林(lin),其(qi)代表(biao)樹(shu)種(zhong)有(you)栲樹(shu)、峨眉栲、刺果米櫧、青(qing)岡、曼青(qing)岡、包(bao)石櫟、華木(mu)(mu)荷、大(da)包(bao)木(mu)(mu)荷、四(si)川(chuan)大(da)頭(tou)茶、楨(zhen)楠(nan)、潤(run)楠(nan)等(deng),海(hai)拔(ba)一(yi)般情況(kuang)下(xia)(xia)在1600~1 800米以下(xia)(xia)。其(qi)次有(you)馬(ma)尾(wei)松、杉(shan)(shan)木(mu)(mu)、柏(bo)木(mu)(mu)組成 的亞熱帶針(zhen)葉(xie)林(lin)及竹林(lin)。 邊緣山(shan)地從下(xia)(xia)而上是(shi)(shi)常綠(lv)闊(kuo)葉(xie)林(lin)、常綠(lv)闊(kuo)葉(xie)與落葉(xie)闊(kuo)葉(xie)混交林(lin),寒溫(wen)帶山(shan)地針(zhen)葉(xie)林(lin),局部有(you)亞高(gao)山(shan)灌叢草甸。
四川(chuan)(chuan)(chuan)盆(pen)(pen)地(di)(di)是中(zhong)(zhong)(zhong)(zhong)國動(dong)(dong)物種(zhong)類最多、最齊全(quan)的地(di)(di)區(qu)之一(yi)。據統計,除魚類外,盆(pen)(pen)地(di)(di)底部共有(you)動(dong)(dong)物417種(zhong),盆(pen)(pen)地(di)(di)西緣(yuan)(yuan)、北緣(yuan)(yuan)和南緣(yuan)(yuan)山地(di)(di)分別為487種(zhong)、317種(zhong)與288種(zhong),其(qi)中(zhong)(zhong)(zhong)(zhong)經濟動(dong)(dong)物均占一(yi)半以上。盆(pen)(pen)地(di)(di)西緣(yuan)(yuan)山地(di)(di)是中(zhong)(zhong)(zhong)(zhong)國特有(you)而古老(lao)動(dong)(dong)物保(bao)存最好、最集(ji)中(zhong)(zhong)(zhong)(zhong)的地(di)(di)區(qu),屬于(yu)一(yi)類保(bao)護動(dong)(dong)物的有(you)大(da)熊貓(mao)、金絲(si)(si)猴、扭角(jiao)羚(ling)(ling)、灰金絲(si)(si)猴、白(bai)唇鹿等(deng)(deng)。還有(you)珍貴特有(you)動(dong)(dong)物小熊貓(mao)、雪豹、鬣羚(ling)(ling)、短尾猴、獼猴、毛冠鹿、水獺及鴛鴦、血雉、紅腹(fu)角(jiao)雉、綠尾虹雉、白(bai)腹(fu)錦雞、紅腹(fu)錦雞等(deng)(deng)。 盆(pen)(pen)地(di)(di)西緣(yuan)(yuan)的平(ping)武(wu)、青川(chuan)(chuan)(chuan)、北川(chuan)(chuan)(chuan)、寶(bao)興、天全(quan)、洪雅、馬(ma)(ma)邊等(deng)(deng)地(di)(di),均為中(zhong)(zhong)(zhong)(zhong)國大(da)熊貓(mao)的主要分布區(qu)。已(yi)設立唐家(jia)河(he)、王朗、臥龍(見臥龍自然保(bao)護區(qu))、蜂桶寨、喇叭(ba)河(he)等(deng)(deng)7處大(da)熊貓(mao)、金絲(si)(si)猴等(deng)(deng)自然保(bao)護區(qu)。 酉(you)陽、馬(ma)(ma)邊、平(ping)武(wu)等(deng)(deng)盆(pen)(pen)地(di)(di)邊緣(yuan)(yuan)山地(di)(di)溪(xi)溝(gou)中(zhong)(zhong)(zhong)(zhong)的大(da)鯢及長(chang)江、金沙江中(zhong)(zhong)(zhong)(zhong)的中(zhong)(zhong)(zhong)(zhong)華鱘(xun)、白(bai)鱘(xun)也為四川(chuan)(chuan)(chuan)所特有(you),均屬國家(jia)保(bao)護動(dong)(dong)物。
四(si)川盆(pen)地有(you)煤、鐵、天然氣、石油、鹽(yan)(yan)、芒硝、石膏、磷、硫、鋁(lv)、金、銅、錳(meng)、石墨(mo)、汞等礦(kuang)產資源,其中(zhong)天然氣、芒硝為(wei)全中(zhong)國之冠(guan),并有(you)中(zhong)國重要的鍶礦(kuang)。川東(dong)北是(shi)世界最大(da)的天然氣富集區之一,川中(zhong)和南充(chong)等地鹽(yan)(yan)巖礦(kuang)儲量很大(da)。
四川盆地(di)地(di)形(xing)閉塞,由(you)于北(bei)部(bu)秦嶺(ling)阻擋冷空氣,冬季氣溫(wen)(wen)高(gao)(gao)于同緯(wei)度(du)(du)(du)(du)(du)其(qi)他地(di)區。最冷月(yue)北(bei)部(bu)均溫(wen)(wen)3~5℃,南(nan)部(bu)5~8℃,較(jiao)同緯(wei)度(du)(du)(du)(du)(du)的上(shang)海、湖北(bei)、安徽及(ji)緯(wei)度(du)(du)(du)(du)(du)偏南(nan)的貴州高(gao)(gao)1~4℃。盆地(di)北(bei)部(bu)極端最低溫(wen)(wen)-8~-5℃,南(nan)部(bu)-5℃~-2℃。霜(shuang)雪(xue)少見,年(nian)無霜(shuang)期長(chang)280~350天,同緯(wei)度(du)(du)(du)(du)(du)上(shang)的武漢冬天卻霜(shuang)雪(xue)不斷,盆地(di)位于長(chang)江河谷中的長(chang)寧(ning)全年(nian)無霜(shuang)。 盆地(di)各地(di)夏(xia)季始于5月(yue)底(di),終于9月(yue)中旬,夏(xia)長(chang)4個(ge)月(yue),溫(wen)(wen)度(du)(du)(du)(du)(du)上(shang)東高(gao)(gao)西低。盆地(di)西部(bu)夏(xia)天平(ping)均氣溫(wen)(wen)約25℃,較(jiao)同緯(wei)度(du)(du)(du)(du)(du)的上(shang)海、武漢等城市偏低3-4度(du)(du)(du)(du)(du),但濕度(du)(du)(du)(du)(du)較(jiao)大(da),所以悶熱難忍。
東(dong)(dong)部最熱(re)月(yue)氣溫(wen)(wen)(wen)高(gao)(gao)達26~29℃,長(chang)江(jiang)河谷(gu)局地達到30℃。盛夏連晴高(gao)(gao)溫(wen)(wen)(wen)天氣又造成盆(pen)(pen)(pen)地東(dong)(dong)南(nan)(nan)部嚴重的夏伏旱。盆(pen)(pen)(pen)地氣溫(wen)(wen)(wen)東(dong)(dong)南(nan)(nan)高(gao)(gao)西(xi)北(bei)低(di),盆(pen)(pen)(pen)底高(gao)(gao)邊(bian)(bian)緣低(di); 各(ge)地年均溫(wen)(wen)(wen)16~18℃。10℃以(yi)(yi)上活動積溫(wen)(wen)(wen)4500~6000℃,持(chi)續期(qi)8~9個(ge)月(yue),屬中亞(ya)熱(re)帶。東(dong)(dong)南(nan)(nan)部的長(chang)江(jiang)河谷(gu)積溫(wen)(wen)(wen)超過6000℃,相當于(yu)中國南(nan)(nan)嶺以(yi)(yi)南(nan)(nan)的南(nan)(nan)亞(ya)熱(re)帶氣候。盆(pen)(pen)(pen)地氣溫(wen)(wen)(wen)東(dong)(dong)高(gao)(gao)西(xi)低(di),南(nan)(nan)高(gao)(gao)北(bei)低(di),盆(pen)(pen)(pen)底高(gao)(gao)而(er)邊(bian)(bian)緣低(di),等溫(wen)(wen)(wen)線分布呈現同(tong)心(xin)圓(yuan)狀。盆(pen)(pen)(pen)地邊(bian)(bian)緣山地氣溫(wen)(wen)(wen)具有垂直分布特點,如峨眉山、金佛山海拔升高(gao)(gao)百米,氣溫(wen)(wen)(wen)遞減0.55℃和0.61℃。峨眉山頂年均溫(wen)(wen)(wen)僅3℃,10℃以(yi)(yi)上活動積溫(wen)(wen)(wen)586℃,氣候上相當于(yu)寒溫(wen)(wen)(wen)帶和亞(ya)寒帶。
四川盆(pen)地(di)(di)年(nian)降水(shui)量(liang)1000~1300毫米(mi),盆(pen)地(di)(di)邊緣(yuan)山(shan)(shan)地(di)(di)降水(shui)十分(fen)充沛,如樂山(shan)(shan)和雅安間的西緣(yuan)山(shan)(shan)地(di)(di)年(nian)降水(shui)量(liang)為(wei)1 500~1800毫米(mi),為(wei)中(zhong)國突出的多雨(yu)(yu)(yu)(yu)區,有(you)“華西雨(yu)(yu)(yu)(yu)屏”之稱(cheng)。但冬干、春旱、夏澇(lao)、秋綿雨(yu)(yu)(yu)(yu),年(nian)內分(fen)配不均,70~75%的雨(yu)(yu)(yu)(yu)量(liang)集(ji)中(zhong)于6~10月(yue)。最(zui)大日(ri)降水(shui)量(liang)可(ke)達(da)300~500毫米(mi)。“巴山(shan)(shan)夜雨(yu)(yu)(yu)(yu)”自(zi)古(gu)聞名,夜雨(yu)(yu)(yu)(yu)占總雨(yu)(yu)(yu)(yu)量(liang)的60~70%以上。盆(pen)地(di)(di)區霧大濕重,云低(di)陰天多。峨眉山(shan)(shan)、金佛山(shan)(shan)是中(zhong)國霧日(ri)最(zui)多地(di)(di)區之一,年(nian)相對濕度之高也為(wei)中(zhong)國之冠。盆(pen)地(di)(di)年(nian)日(ri)照僅900~1300小時,年(nian)太(tai)陽(yang)輻(fu)射量(liang)為(wei)370~420千焦耳/平方厘米(mi),均為(wei)中(zhong)國最(zui)低(di)值,故有(you)“蜀犬吠(fei)日(ri)”之說。